Medical balloons are used in a number of areas in treatment of humans and animals. For example, balloons are used during delivery of medical devices such as stents. A deflated balloon is positioned inside a stent and the package is positioned in a lumen that the stent is to support. The balloon is inflated which causes the stent to expand into a deployed state. The balloon can then be deflated and removed, leaving the deployed stent in place.
Embodiments of the present invention concern medical balloons that are designed for use in pumping. Preferred embodiments concern intra-aortic balloons for use in intra-aortic balloon pumps. IABs are well known for use in treating patients with heart failure and other cardiac pathologies, in order to increase blood flow to coronary arteries and decrease ventricular load.
The two main benefits of the IAB therapy are achieved as follows:                1) To increase flow to the coronary artery. This benefit is achieved through balloon inflation, which results in displacing an amount of blood towards the ascending aorta, increasing the pressure at the coronary sinus, and hence enhancing the flow to the coronary arteries.        2) To decrease the load against which the heart pumps. This benefit is achieved through balloon deflation, which reduces the pressure at the root of the aorta. Consequently, when the aortic valve opens, the heart experiences less pressure which reduces the mechanical work required by the heart to eject its blood output into the aorta. This also reduces the amount of oxygen required by the heart muscle and may allow it to rest.        
An IAB is used to operate as a pump; inflation and deflation causes blood to flow predominantly towards and away from the left ventricle respectively. This pump acts as a mechanical device that is operated to increase coronary flow and therefore improve myocardial oxygen delivery. The IAB is typically connected via a catheter to an external pump. The IAB is inflated and deflated in synchronisation with heartbeats, in a manner known as counter-pulsation. Typically, the IAB is inflated in early diastole (i.e. immediately following closure of the aortic valve) in order to displace blood towards the coronary arteries. It is considered that a balloon is more efficient if it can maximise this fluid towards the ascending aorta.
The IAB is typically then deflated in late diastole (i.e. immediately prior to the left ventricle's contraction) to reduce the load (afterload) and hence reduces ventricular oxygen.
The IAB is normally introduced into the body at a site remote of the heart such as the groin and then guided up the aorta towards the heart. The IAB is packaged in such a way as to minimise its profile to allow for insertion from the femoral artery. The catheter that is attached to the IAB is used to provide fluid (typically helium which is selected due to its low viscosity and inert nature) for inflation and deflation.
The hydrostatic pressure experienced along the length of conventional, nominally cylindrical IABs, inserted into the aorta of an inclined patient, causes them to inflate from top to bottom (proximal from and distal to the heart respectively). The inventor of the present application has also observed that this combination of pressure gradient and shape will displace less blood towards the heart than is desirable. As such, it is common for conventional prior art IABs to provide reduced efficacy in the inclined patient. These observations were first noted by the inventor in the publication Khir A W, Price S, Hale C, Young D A, Parker K H, Pepper J R. Intra-Aortic Balloon Pumping: Does Posture Matter? Artif Organs, 29: 36-40, 2005.
One particular issue with IAB treatment is the possibility of mechanical damage to blood cells. As the IAB is inflated or deflated, displacement pressures and/or pumping/suction forces are applied to blood cells. If these or their rates are too extreme, it may result in damage to the blood cells. There is also a risk that blood cells may be trapped between the IAB and a vessel wall if the IAB is operated to occlude the passage or vessel. A blood cell may burst if subjected to pressures of above or lower than 200 Pa.
In the present application, certain terms are used and should be understood as follows:                intra-aortic balloon (IAB), the device inserted into a patient's aorta        first end of an IAB, the lower end, bottom or base, distal from the heart (the end at which the catheter connects)        second end of an IAB, the upper end, top or tip, proximal to the heart (the opposite end from the catheter connection)        length of an IAB, the longitudinal length of an IAB        length of a tapered section; the length, from the start of the taper to the point where the taper ends (for example, where it makes a point at an end of the balloon or where the balloon walls become non-tapering), along the longitudinal axis of an IAB        intra-aortic balloon pump (IABP); the instrument external to the patient that pumps gas (usually helium) to an IAB via a catheter. It will be appreciated that there are effectively two “pumps” in an IABP: the external pump that supplies the gas via the catheter to the IAB, and, the IAB itself which when inflated and deflated in the aorta causes pumping of blood.        inflation; the expansion of the cross-sectional area of an IAB when pressurised gas is pumped into its internal chamber(s)        fully inflated; the state of the balloon when its walls are completely inflated to reach their sectional nominal dimensions in response to the standard manufacturer inflation pressure or higher.        pump/pumping; the pumping effect exerted by an IAB on blood in the aorta.        